The present invention relates to an assembly for the actuation of an in-line valve, and preferably a starter valve, and the indication for its opened or closed status.
In gas turbine engines, such as is used in airplane engines, high-pressure air is delivered to an air driven engine starter motor. In some of these engines, this air flow is controlled by an in-line starter valve. The starter valve operates in a high temperature environment that is high (in some cases on the order of 400 to 450 degrees Fahrenheit) due to its proximity to the engine and the temperature of the high-pressure air that it controls. Typically, the valve is pneumatically activated by pressure exerted from a pneumatic chamber, but an external wrenching mechanism is provided to permit manual actuation. For purposes of this application, it should be understood that the “manual” application could be driven by a power tool or other device that does not impede valve motion during normal conditions. The wrenching mechanism also serves as the valve position indicator as the valve position may be determined by comparing the angular position of an index mark on the manual wrench shaft to “open” and “close” marks on the outside of the valve housing.
When the valve is pneumatically activated, the wrenching mechanism is free to turn in a back driven motion dictated by the motion of the valve piston. The wrenching mechanism is lightly loaded resisted only by the friction of the mechanism itself and the spring force built into the system. In the event that the valve is manually activated, the wrenching mechanism must be capable of exerting a strong pull (in some cases on the order of a 300 pound pull) on the valve piston in a worst case condition to overcome duct air pressure that tends to hold the valve closed.
Typically the wrenching mechanism includes a “rack and pinion” assembly. However, using these assemblies in this application is costly, and of a relatively heavy weight, subject to jamming, and not very durable. These assemblies typically require routine lubricating maintenance to reduce gear wear and further are subject to backlash, which necessitates the use of a torsion spring along the manually operated shaft.
It would be desirable to provide an in-line starter valve with a manually operable wrenching assembly that eliminates the potential for jamming and backlash and does not have gears that would require lubricating maintenance. It would further be desirable for the in-line starter valve to be equipped with an assembly that is less costly to produce and lighter in weight than the rack and pinion assembly while at the same time affords greater durability and is able to withstand elevated temperatures.